Lymph Node

The lymph node is associated with afferent and efferent lymphatic vessels. It is surrounded by a capsule, has trabeculae, and can be divided into outer cortical, inner cortical (paracortical), and medullary regions (Figure 1-4-2):

■ The outer cortex contains most of the nodules and germinal centers. It is populated by most of the B lymphocytes.

• The inner cortex is populated by T lymphocytes.

Lymphoid Organs

Figure 1-4-3. Spleen Schematic

Sinuses

Figure 1-4-3. Spleen Schematic

Chapter Summary

The thymus contains trabecule and has a cortical and medullary region. Epithelial reticular cells and Hassall's corpuscles are located within the medulla. The cortex lacks germinal centers. The thymus protects developing T cells by the blood-thymus barrier.

The lymph node has three layers: cortical (outer and inner, i.e., paracortical and medullary), The outer cortical layer contains most of the nodules and germinal centers. Most of the tf lymphocytes reside here, whereas T lymphocytes reside in the paracortical layer. Dendritic cells within lymph nodes are antigen-presenting cells. High endothelial venules are the site of repopulation of lymph nodes and are located within the paracortical zones.

The spleen is very vascular and has red and white pulp. White pulp is composed of lymphoid tissue. T lymphocytes are located in the periarterial sheaths, while peripheral white pulp and germinal centers contain B lymphocytes. Red pulp consists of splenic cords and venous sinusoids. Its function is to delay passage of defective red blood cells to enable their elimination through phagocytosis by macrophages.

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